1. Technical Field
The present invention relates to a flexible packaging material that can be used in packaging food products and to a method of making the packaging material. More specifically it relates to forming a removable strip that is cut from one or more layers and can be removed without harming the rest of the packaging material. Even more specifically, the present invention relates to using a removable strip of the packaging material to provide removable promotional material (with or without the promotional material being visible prior to removal of the strip), removable stickers, or an adhesive area for re-closing the package.
2. Description of Related Art
Snack foods and other items are often packaged in bags formed from thin, flexible packaging films. These thin films are formed primarily of plastics, such as polypropylene and polyethylene, but can also contain metalized films, foil, paper, or oriented films. These packaging films can have numerous layers directed to achieving specific needs, but are generally formed at least in part by extrusion of a plastic layer, co-extrusion of multiple layers simultaneously, extrusion coating of another material (such as paper), and the lamination of two layers together via either extrusion lamination or adhesive lamination. In the discussions below, both extrusion lamination and adhesive lamination processes are discussed in more detail, but it is noted that any designated layer that is fed into these two processes can already be a multi-layer film formed by any of the above processes.
An exemplary film 100 for packaging of food products is seen in FIG. 1. The outermost layer 102 is an OPP layer, short for oriented polypropylene, while the innermost layer 106 is a metalized OPP. An oriented polymer material has been specially treated so that the long polymeric molecules tend to align in a given direction, causing the material to preferentially tear in that direction. Sandwiched between the two OPP layers 102, 106 is a layer of polyethylene 104, formed as the two OPP layers are extrusion laminated together. Printing for the package is done on the inside of the outer layer and becomes sandwiched between the middle and outer layers. The innermost, metallic layer 106 can itself be a layered laminate and contains a sealant layer 108 on what will be the inside of the package. This sealant layer is formed of a ter-polymer, composed of ethylene, propylene, and butylenes, and provides a barrier to retain taste and freshness. Other materials used in packaging are polyester, paper, polyolefin extrusions, adhesive laminates, and other such materials, or a layered combination of the above.
FIG. 2 demonstrates schematically the formation of material 100, in which the OPP layers 102, 106 of the packaging material are separately manufactured, then formed into the final material 100 on an extrusion laminator 200. OPP layer 102 is fed from roll 201 while OPP layer 106 is fed from roll 205. At the same time, resin for PE laminate layer 104 is fed into hopper 218 and through extruder 216, where it will be heated to approximately 600° F. and extruded at die 214 as molten polyethylene 104. This molten polyethylene 104 is extruded at a rate that is congruent with the rate at which the OPP materials 102, 106 are fed, becoming sandwiched between these two materials. The layered material 100 then runs between chill drum 210 and nip roller 212, ensuring that it forms an even layer as it is cooled. The pressure between the laminator rollers is generally set in the range of 0.5 to 5 pounds per linear inch across the width of the material. The large chill drum 210 is made of stainless steel and is cooled to about 50–60° F., so that while the material is cooled quickly, no condensation is allowed to form. The smaller nip roller 212 is generally formed of rubber or another resilient material. The nip roller 212 wears out fairly quickly and is regularly replaced, while the chill drum 210 is changed much less frequently. Note that the layered material 100 remains in contact with the chill drum 210 for a period of time after it has passed through the rollers, to allow time for the resin to cool sufficiently. The material can then be wound into rolls (not specifically shown) for transport to the location where it will be used in packaging. Generally, it is economical to form the material as wide sheets that are then slit using thin slitter knives into the desired width as the material is rolled for shipping.
Once the material is formed and cut into desired widths, it can be loaded into a vertical form, fill, and seal machine to be used in packaging the many products that are packaged using this method. FIG. 3 shows an exemplary vertical form, fill, and seal machine that can be used to package snack foods, such as chips. This drawing is simplified, and does not show the cabinet and support structures that typically surround such a machine, but it demonstrates the working of the machine well. Packaging film 310 is taken from a roll 312 of film and passed through tensioners 314 that keep it taut. The film then passes over a former 316, which directs the film as it forms a vertical tube around a product delivery cylinder 318. This product delivery cylinder 318 normally has either a round or a somewhat oval cross-section. As the tube of packaging material is pulled downward by drive belts 320, the edges of the film are sealed along its length by a vertical sealer 322, forming a back seal 324. The machine then applies a pair of heat-sealing jaws 326 against the tube to form a transverse seal 328. This transverse seal 328 acts as the top seal on the bag 330 below the sealing jaws 326 and the bottom seal on the bag 332 being filled and formed above the jaws 326. After the transverse seal 328 has been formed, a cut is made across the sealed area to separate the finished bag 330 below the seal 328 from the partially completed bag 332 above the seal. The film tube is then pushed downward to draw out another package length. Before the sealing jaws form each transverse seal, the product to be packaged is dropped through the product delivery cylinder 318 and is held within the tube above the transverse seal 328.
The form, fill, and seal machines are quite expensive, in the range of $250,000 each, but pay for themselves easily when compared to the cost of pre-formed bags and the machinery to fill them. However, in order to maximize the productivity of the form, fill, and seal machines, it is common for the product delivery tube 318 and former 316 to be made as a unit that is easily interchangeable, so that different size packages can be made by the same machine. The length of the transverse seal can also be changed, by exchanging the sealing jaws 326, or in some cases, merely by exchanging their facings (the portion of the sealing jaws which actually makes contact with the packaging film). By changing these elements, as well as the width of film roll feeding into the machine and the programming of the machine, one form, fill, and seal machine can handle a number of different products in different size packages, limited primarily by the width of film the machine will handle, the maximum length of bag the machine is designed to handle, and the available former/delivery tube assemblies.
Although there is no one perfect package for all uses, there are a number of desirable features that manufacturers have long desired to include in packages made on a vertical form, fill, and seal machine. One exemplary feature is the ability to re-close a package of a snack food that is only partially eaten, so that the flavor and texture of the product are preserved as long as possible. High quality reclosable seals, also known as zipper seals, have been introduced in recent times, but these add significantly to the cost of making the bag. It would be desirable to have a low-cost alternative.
Similarly, it can be desirable to include promotional material with a bag of snack food, such as prize announcements, coupons, stickers, or informational graphics. Including such information inside the package can be a problem, however, as the ink and solvent levels in fatty food packages are regulated to insure product safety. If promotional material is included inside the package, it must be enclosed in an impermeable film, which adds to the cost. Dropping promotional material into the package also creates problems, as it may interfere with the normal flow of product and can set off foreign object detectors, costing time. The promotional material can alternatively be provided as part of the graphics seen on the outside of the package, but detachment of the material from the package is not possible without destroying the package itself, so the product must be gone before the promotional material can be removed.
In summary, two desirable options for flexible packaging are currently unavailable: a low-cost re-closing mechanism and the ability to provide promotional material that can be removed without destroying the package.